As long as Italy stays untouched, things should be fine. Probably it would have been different with a different outcome at the battle of Verona. Don’t be so sure, not every family is a happy one… Keep in minds a couple of things: Valens is a freshman and he is not the leader of the war. Of course his link to the imperial family means that everyone who dislike Theodosius enough would probably rally behind him. There is also the question of how both Valens and Theodosius will react to each other. Is Valens ambitious enough to try to usurp the throne? Is Theodosius like his father and grandfather, a man who relies on the members of the imperial family (both main and “cadet” branch)? Don’t forget all those people wielding enough power to influence both the emperor, Valens and the aristocracy: Anicia Eudoxia, Iulia Galla and her husband Belisarius, Serena, Eusebia and her uncle Eleutherius and finally the Eastern branch of the family (Procopius and his sons). The next years are going to be pretty intricate.